1. Field of the Invention
The present invention relates to a method of continuously hot-rolling a multiplicity of sheet bars such as steel slabs, billets, blooms or the like, or sheet bars composed of other metals.
2. Related Art Statement
Hitherto, hot-rolling lines have been so arranged that individual sheet bars are roughly rolled, and are then finish hot-rolled one by one to a predetermined thickness. However, such hot-rolling encounters line stoppage problems if the raw steel material to be rolled is defectively caught at the time of the hot finish rolling process. What is even worse, the yield seriously deteriorates in the event of defective shaping of the leading portion or the trailing portion of the steel or other raw material to be rolled.
In order to overcome these problems a rolling method has been employed in which the front end portion and the rear end portion of the steel sheet bars are joined together prior to performing hot finish rolling, and the joined steel plate is continuously supplied to the hot-rolling line (for example, Japanese Patent Laid-Open No. 61-144203).
As disclosed in Japanese Patent Laid-Open No. 61 -144203 the rear end portion of a leading sheet bar is conveyed forward and the front end portion of the trailing sheet bar which is conveyed behind it are abutted completely against each other, their respective widthwise edge portions are joined up, and the joined sheet bars are rolled while maintaining this configuration.
However, too much time is taken to complete joining with sufficient strength; accordingly, the length of the sheet bar line becomes excessive.
In order to overcome the problem, the inventors of the present invention have disclosed a joining method in International Publication No. WO92/02313, No. WO92/02314 and No. WO92/02315, the joining method being so conducted that the rear end portion of the leading sheet bar and the front end portion of the trailing sheet bar are partially cut so as to bring at least the two widthwise edge portions of the two sheet bars into contact with each other, a gap is created between the two sheet bars, and the contact portions are locally heated and pressed. As a result, the joining work can be more quickly and easily performed.
However, the aforesaid method is subject to further improvement because breakage and separation where the sheet bars are joined up cannot be completely prevented due to a fact that the gap between the two sheet bars cannot be completely eliminated in the hot-rolling process.